Meter with small tilt error

ABSTRACT

An induction type meter has a rotor mounted for rotation about a vertical axis and supported vertically by a magnetic mounting. The rotor is restrained against lateral motion by ring bearings made of an aromatic polyimide resin and a filler.

United States Patent m Ill 15] 3,693,086 Redecker et al. [4 1 Sept. 19,1972 METER WITH SMALL TILT ERROR 3,453,208 7/1969 Gallagher ..252/l2[72] Inventors: Henry W. Redecker, Rt. 6; Eugene o. Bezgela, 351 ForsythSt., both of OTHER PUBLICAnoNS a g 27609 Devine et al., AromaticPolyimide Compositions For [22] Filed: March 15 1971 gglsid gigrication,Lubrication Engr. June 1964, pg. 21 Appl. No.1 124,425

' Primary EQmminer--Alfred E. Smith Related US. Application Data Stratum[63 I Continuation of Ser. No. 746,641, July 22,

. I968, abandoned. [57] ABSTRACT An induction type meter has a rotormounted for rota- [52] US. Cl ..324/155, 252/12 ion about a verticalaxis and supported venically'by a {51] Int. Cl. ..G0lr 1/00 magneticmounting. The rotor is restrained against [58] Field of Search..324/155; 252/12 latera] motion by ring bearings made of an aromaticpolyimide resin and a filler. [56] References Cited 5 Claims, 2 DrawingFigures UNITED STATES PATENTS 3,143,704 8/1964 Wright ..324/l55PAIENTEDsEP 19 m2 I l ll WITNESSES INVENTORS Henry W. Redecker W W My WMETER WITH SMALL TILT ERROR BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates to a measuring device having a rotorarranged for continuous rotation about a vertical axis, and it relatesparticularly to an induction type watthour meter having magneticmounting and having ring bearings.

Although the invention is applicable to various measuring devices havingrotors arranged for rotation, it is particularly suitable for inductiontype watthour meters and will be described as applied to such a meter.

2. Description of the Prior Art For many years the induction typewatthour meter has employed a rotor mounted for rotation about avertical axis and supported by a magnetic mounting. The rotor ismaintained in vertical alignment by means of guide bushings or ringbearings of graphite which coact with chrome or stainless steel guidepins. Such meters are described in the Electrical Metermen's Handbook,Seventh Edition, Published in 1965 by Edison Electric Institute, NewYork City.

One of the troubles encountered with graphite journal bearings or guidebushings is that of tilt instability. When the axis of the rotor departsfrom the vertical or is tilted, a tilt performance error is introducedwhich changes with operating time.

The change in tilt performance for graphite journal bearings is causedat least in part by the graphite changing its surface condition due towar and thereby changing its coefficient of friction, particularly atvery low loads. In addition to the changing surface condition, thegraphite also has a nonlinear coefficient of friction curve with respectto load, particularly very light loads. Since the meter tilt instabilityis occurring at low driving torques and variable low bearing loads,graphite does not provide ideal performance.

Much effort has been expended in attempting to improve the ring bearing.In U.S. Pat. Nos. 2,953,415 and 2,965,418 reference is made topolyurethane synthetic resins and synthetic linear polyamide resins. Thepolyu rethane resin may be mixed with modifying agents such as graphite,powdered mica or asbestos.

In the patent application of Merrion D. Gill and Eugene G. Bezgela, Ser.No. 376,940, filed June 22, 1964, now U.S. Pat. No. 3,397,929, assignedto the same assignee, reference is made to polycarbonate, crystallizedacetal resin, nylon and fluorocarbon.

SUMMARY OF THE INVENTION In accordance with the invention, a fillerhaving good low-friction properties is added to a base material havinggood mechanical, thermal and chemical properties. In a preferredembodiment of the invention the filler is a fluorocarbon material andthe base material is an arcmatic polyimide resin. A ring bearing orbushing formed of the resultant material for induction meters not onlydisplays excellent tilt stability but possessed other propertiesdesirable for such a hearing or bushing.

It is therefore an object of the invention to provide a bearing for avertical shaft which has good tilt stability.

It is also an object of the invention to provide an induction meterhaving a rotor mounted for rotation about a vertical axis by a magneticmounting and ring bearings having good tilt stability.

It is another object of the invention to provide an induction meter asrecited in the preceding paragraph wherein the ring bearings areconstructed of a material containing a polyimide.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects will be apparent fromthe following description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a view in front elevation with parts broken away of a watthourmeter embodying the invention; and

FIG. 2 is a view in side elevation with parts broken away showing therotor assembly and associated parts of the watthour meter of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to simplify thepresentation, the invention will be described as applied to the watthourmeter of the Wright U.S. Pat. No. 3,143,704, issued Aug. 4, I964. FIGS.1 and 2 are reproductions of, and employ similar reference charactersfor designating components similar to those of, FIGS. 1 and 2 of theWright patent. For convenience, the components are listed as follows:

1 Induction type watthour meter 2 Base 5 Glass cover 7 Magneticstructure 9 Voltage section 9A Voltage pole 98 Voltage winding 11Current section 1 IA, 1 18 Current poles 11C, 11D Current windings I3Electroconductive disc or armature l5 Shaft 17 Upper bearing assembly I9Lower bearing assembly 21 Frame 23, 25 Set Screws 27, 29 Damping magnets31 Hub 35 Worm 37 Worm wheel 38 Cup-shaped recess 39, 47 Ring bearings41, 49 Stainless steel pins 43, 51 Sleeves Die casting alloy 53, 55Permanent magnets 57, 61 Steel cups 59 Solder The components 7, 9, 9A,9B, 1 l, l1A-llD form parts of an electromagnet which, when energized,applies a shifting magnetic field to the armature 13.

Except for the ring bearings 39 and 47, the structure of FIGS. 1 and 2is identical to that of FIGS. 1 and 2 of the Wright patent. In theWright patent the ring bearings are constructed of graphite. Thismaterial has given generally good performance. As previously noted, theperformance of graphite in the field of tilt performance leavessomething to be desired.

To illustrate the qualities desired in a ring bearing for an inductionmeter the following items are listed:

I Low friction.

2. Tilt error within the limits of the MSJ-lO test. Test points arereference (vertical), 4 top to front, 4 top to back, 4 top to left and 4top to right. See Test No. 15, EEI Pub. No. MSJl-1966-AE- IC-AlEE-NEMAStandards for watthour Meters. Edison Electric Institute, New York City,is one of the sponsors.

3. Repetition of item 2 after operation of the meter for a period oftime at maximum overloads.

4. Operation with a PV factor (bearing pressure multiplied by bearingvelocity) several times maximum rating should not produce excessive wearor error.

5. Operation at elevated temperatures should not produce excessive wearor error.

6.,Operation at elevated humidity and temperature should not produceexcessive wear or error.

Other criteria such as machinability or moldability, resistance tosolvents such as chloroethene, alcohols, and trichloroethyleneresistance to ultra-violet radiation and resistance to corrosion are ofimportance.

' The materials tested included base materials such as polycarbonate,acetyl, epoxy, fluorocarbons, polyamide, phenolic polyurethane, andaromatic polyimide materials, and fillers such as ceramic, graphite,bronze, molybdenum disulphide, glass and fluorocarbon materials. Of thebase materials the aromatic polyimide material was outstanding.

Examples of aromatic polyimide resins are found in US. Pat. Nos.3,179,630 to 3,179,634 inclusive and 3,179,614. An example of anaromatic polyamide imide resin is found in US. Pat. No. 3,179,635.Lubricant films composed of MoS Sb O bonded with polyimide resins arediscussed in Lubrication Engineering, July, 1967, pgs. 288-294. Aromaticpolyimides filled with WSe, MoS and graphite are discussed as lubricantsfor ball bearings in Lubrication Engineering, June 1964, pgs. 225230.

A base material formed of an aromatic polyimide constitutes an extremelystable matrix which is resistant to solvents and ultra-violet radiation.

For a filler a fluorocarbon polymer has been found to be highlydesirable. An example of a fluorocarbon polymer ispolytrifluoromonochloroethylene which is available under the trade nameKel-F.

The aromatic polyimide resin is employed as a matrix to hold the fillereffectively in position. A preferred fluorocarbon polymer ispolytetrafluoroethylene which is available under the trade name Teflon.The filler has exceptionally low friction properties in a ring bearing.It is our theory that this low friction is due in at least part to atransfer of fluorocarbon polymer from the ring bearing to deposit on thechrome or stainless steel pins 41, 49, so that in effect a fluorocarbonpolymer coated pin rotates in a fluorocarbon-polymer-containing ringbearing.

We presently prefer to employ a filler comprising 30 to 45 percent byweight of the polyimide resin but fillers outside this range (such as ina range of 4 to 80 percent) may be employed. The filler may be mixed infinely divided or powdered form (for example a powder particle size of kto microns or smaller) into an aromatic polyimide liquid or varnish.After it has hardened, the resultant material may be used in sheet formor ground into a powder and sintered into the desired shape.

A polyimide material is listed for non-lubricated bearings under thetrade name Meldin Pl-30X in various molded shapes by the DixonCorporation, Bristol, Rhode Island and under the trade name Vespel bythe El. du Pont de Nemours & Co. (Inc.). Wilmington, Delaware. Inasmuchas it is machinable it may be procured in sheet form and the ringbearings then may be machined from the sheet.

The fluorocarbon polymer alone tends to creep or cold flow underpressure and does not machine well. However, the aromatic polyimideresin addition causes the resultant material to resist cold flow and tobe readily machinable. Furthermore the material may be employed atelevated temperatures, such as 125 C. or more. It is highly resistant tocorrosion, humidity, solvents and ultra-violet radiation. It alsowithstands cold running at 40 C. and cycling between 40 and 125 C.

The pins 41, 49 may be of other resilientmaterial such as berylliumcopper. However, stainless steel is preferred, in part because of itsresistance to corrosion.

To illustrate the performance of the invention MSJ-lO light-load testswere conducted on induction watthour meters 3 and 4 which were similarto those shown in the aforesaid Wright patent and on induction watthourmeters 1 and 2 which were similar to themeters 3 and 4 except that thegraphite ring bearings were replaced by the aromatic polyimide resin andpolytetrafluoroethylene filler ring bearings described above. Theresults of the tests are compiled in Table I below, and show the muchgreater stability and the lower maximum per cent error of the ringbearings of the invention.

TABLE I Percent error Percent error Meter Meter Meter Meter No. 1 N0. 2No. 3 No. 4

4 Tilt, top to front:

Start .28 .28 87 .54 22 51 72 .33 1.69 97 27 1.65 1.06 26 1.32 .86

After 35 days .45 1.05 .60 4 'Illt top to roar:

Start +.03 -.12 +1.55 +.85 After 7 days. +.03 00 68 +1.03 After 14 days10 03 +1.47 99 After 21 days 00 04 +1.15 25 After 28 days .01 06 22 20After 35 days +.05 .09 .09 +.9J 4 'lilt top to left:

Start 32 39 40 76 After 7 days. 39 +.43 --1.80 00 After 14 days 44 431.06 +.22 After 21 days 41 44 1. 77 05 After 28 days 43 +.48 -1. 66 -.04After 35 days. 60 36 +1.55 1 'lllt top to rlght:

Start .45 -.2.) +.41 +.11 46 -.34 +.03 53 36 --.34 +1. 26 52 52 -.43 8825 .46 .40 .02 18 After 35 days .47 -.28 -.07 +.35

An aromatic polyimide resin lubricating film and bearing surface iscovered in the copending patent application of William M. Alvino andJames H. Freeman, Ser. No. 724,728, filed Apr. 29, 1968, now US. Pat.No. 3,608,054 and assigned to the same assignee.

We claim as our invention:

1. An induction meter, comprising:

a stator assembly including an electromagnet having spaced voltage andcurrent poles,

a rotor assembly including an electrically conductive disc disposedbetween the spaced voltage and current poles, bearing means mountingsaid rotor assembly for rotation about a substantially vertical axisrelative to the stator assembly, said bearing means including means forrestraining said rotor assembly from lateral movement relative to thestator assembly, comprising a ring bearing and a pin rotatably receivedby the ring bearing, with the axis of said'pin being substantiallyvertical, said ring bearing having base material comprising a matrixconstructed essentially of an aromatic polyimide resin, and a lubricantfiller in the matrix. 2. The induction meter of claim 1 wherein thebearing means includes a magnetic mounting for providing verticalsupport for the rotor assembly.

3. The induction meter of claim 1 wherein the pin is a corrosionresistant metal and the lubricant filler is es sentially a fluorocarbonpolymer.

4. The induction meter of claim 1 wherein the lubricant filler isessentially polytetrafluoroethylene.

5. The induction meter of claim 2 wherein said rotor assembly includes ashaft, wherein said ring bearing and pin form one mounting arrangementat one end of said shaft, and wherein a second substantially identicalring bearing and pin form another mounting arrangement at an oppositeend of said shaft for mounting said rotor assembly to said statorassembly

2. The induction meter of claim 1 wherein the bearing means includes amagnetic mounting for providing vertical support for the rotor assembly.3. The induction meter of claim 1 wherein the pin is a corrosionresistant metal and the lubricant filler is essentially a fluorocarbonpolymer.
 4. The induction meter of claim 1 wherein the lubricant filleris essentially polytetrafluoroethylene.
 5. The induction meter of claim2 wherein said rotor assembly includes a shaft, wherein said ringbearing and pin form one mounting arrangement at one end of said shaft,and wherein a second substantially identical ring bearing and pin formanother mounting arrangement at an opposite end of said shaft formounting said rotor assembly to said stator assembly.